首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2527篇
  免费   175篇
  国内免费   37篇
耳鼻咽喉   8篇
儿科学   86篇
妇产科学   66篇
基础医学   255篇
口腔科学   51篇
临床医学   610篇
内科学   345篇
皮肤病学   30篇
神经病学   246篇
特种医学   199篇
外科学   262篇
综合类   63篇
预防医学   144篇
眼科学   103篇
药学   138篇
中国医学   2篇
肿瘤学   131篇
  2023年   14篇
  2022年   13篇
  2021年   40篇
  2020年   19篇
  2019年   31篇
  2018年   52篇
  2017年   27篇
  2016年   37篇
  2015年   54篇
  2014年   74篇
  2013年   85篇
  2012年   88篇
  2011年   84篇
  2010年   63篇
  2009年   68篇
  2008年   71篇
  2007年   71篇
  2006年   66篇
  2005年   64篇
  2004年   70篇
  2003年   75篇
  2002年   70篇
  2001年   84篇
  2000年   72篇
  1999年   78篇
  1998年   110篇
  1997年   108篇
  1996年   94篇
  1995年   87篇
  1994年   59篇
  1993年   63篇
  1992年   47篇
  1991年   45篇
  1990年   47篇
  1989年   39篇
  1988年   58篇
  1987年   41篇
  1986年   45篇
  1985年   50篇
  1984年   35篇
  1983年   29篇
  1982年   20篇
  1981年   21篇
  1980年   17篇
  1979年   29篇
  1978年   17篇
  1977年   17篇
  1976年   20篇
  1974年   13篇
  1969年   15篇
排序方式: 共有2739条查询结果,搜索用时 15 毫秒
61.
The investigators designed this validation study to determine the defining characteristics of the nursing diagnosis ineffective airway clearance. Using Fehring's Diagnostic Content Validity Model, 546 nurses who care for respiratory clients validated one major and 19 minor defining characteristics. Nine characteristics previously described in the literature were eliminated. Clarification of the defining characteristics of this diagnosis improves communication in practice, education and research.  相似文献   
62.
Book Review     
Performance Breakthroughs for Adolescents With Learning Disabilities or ADD. G. Markel & J. Greenbaum.  相似文献   
63.
64.
Rodgers  GM; Greenberg  CS; Shuman  MA 《Blood》1983,61(6):1155-1162
The coagulant properties of intact bovine vascular cells (aortic endothelial and smooth muscle cells) and human vascular cells (cutaneous and foreskin microvascular cells, umbilical venous endothelium) grown in vitro were studied. Compared to nonvascular cells (fibroblasts, corneal endothelial cells, fetal lung or intestinal mucosal cells), vascular cells had little procoagulant activity. Radioimmunologic measurement of thrombin in recalcified plasma demonstrated markedly lower concentrations of thrombin in the presence of vascular endothelial and smooth muscle cells compared to corneal endothelial and fetal lung cells. The low thrombin concentrations were not a consequence of thrombin binding to the vascular cells nor were they due to accelerated thrombin inactivation by antithrombin-III or alpha 2-macroglobulin. Neither vascular cells nor the nonvascular cells promoted contact activation of plasma as measured by a sensitive specific assay for kallikrein. Studies with intact cell monolayers and purified factors VIIa and X indicated that while nonvascular cells express tissue factor activity, vascular cells do not exhibit this property. These data suggest that the nonthrombogenic nature of intact vascular cells is due to their failure to initiate contact activation and to express tissue factor activity. In addition, the primary difference in coagulant potential between vascular cells and nonvascular cells is the lack of tissue factor expression by the vascular cells.  相似文献   
65.
66.
Chang  CS; Sassa  S 《Blood》1985,65(4):939-944
Physicochemical and immunologic properties of delta-aminolevulinate (ALA) dehydratase in human K562 erythroleukemia cells were examined. ALA dehydratase activity was found to increase in K562 cells after treatment with butyric acid or selenium oxide. Enzyme activity in untreated K562 cells was comparable to that in normal adult erythrocytes but was increased three- to six-fold in K562 cells treated with 1.2 mmol/L butyric acid or 0.03 mmol/L selenium oxide. The Michaelis-Menten constant (Km), the inhibitor constant (Ki), and elution profile by diethylaminoethyl (DEAE) cellulose chromatography were similar for ALA dehydratase from K562 cells and normal human adult and human fetal erythrocytes. However, ALA dehydratase from K562 cells did not react with a monospecific rabbit antibody against ALA dehydratase purified from normal adult erythrocytes, although the antibody reacted with the enzyme from normal adult and fetal red cells. These findings indicate that ALA dehydratase in K562 cells is immunologically distinct from the normal enzyme.  相似文献   
67.
68.
To fully understand the role of diet diversity on allergy outcomes and to set standards for conducting research in this field, the European Academy of Allergy and Clinical Immunology Task Force on Diet and Immunomodulation has systematically explored the association between diet diversity and allergy outcomes. In addition, a detailed narrative review of information on diet quality and diet patterns as they pertain to allergic outcomes is presented. Overall, we recommend that infants of any risk category for allergic disease should have a diverse diet, given no evidence of harm and some potential association of benefit in the prevention of particular allergic outcomes. In order to harmonize methods for future data collection and reporting, the task force members propose relevant definitions and important factors for consideration, when measuring diet diversity in the context of allergy. Consensus was achieved on practice points through the Delphi method. It is hoped that the definitions and considerations described herein will also enable better comparison of future studies and improve mechanistic studies and pathway analysis to understand how diet diversity modulates allergic outcomes.  相似文献   
69.

The aim of this study was to analyze whether different fixation methods such as freezing or formaldehyde storage for different periods of time have an influence on the recognition of anatomical relevant structures in the middle and inner ear of the cat with conventional computed tomography (cCT) and micro-computed tomography (µCT). Besides, effects of freeze–thaw cycles on determined structures of the ear were investigated by means of histological slices. Three veterinarians with different radiologic expertise evaluated the scans of 30 dissected cat ears anonymously and scored predefined structures in a five-point scale with reference to visually sharp reproducibility and perfect image quality. The total scores of the different fixation groups as well as the ears within a group were compared with each other. Furthermore, an intra-reader examination including an evaluation of the identifiability of specified structures was performed for both imaging methods. cCT as well as µCT-scans have a very low variation coefficient of 1.6% and 2.3%, respectively. The results for the alterations between the different fixation methods show that the changes for cCT-scans are negligible, as the percentage alteration compared to fresh samples ranges in a very small interval with values from 1.0% better to 1.2% worse. µCT-scans are more influenced by the fixation method with a range from 1.3% better to 6.9% worse values. The scans mostly deteriorated after two freeze–thaw cycles (1.8% worse) and after storing the samples for 1 (2.4% worse), respectively, and 3 weeks in formaldehyde (6.9% worse).

  相似文献   
70.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号